The objective is to characterize and understand the in vivo behavior of ultrahigh molecular weight polyethylene (UHMWPE), a material which is extensively used in total joint prostheses particularly of the knee and hip; and by this knowledge to develop substantially improved versions of this material in order to avoid the real and potential clinical problems which are the result of in vivo wear and mechanical deterioration. There is evidence of excessive wear in vivo of UHMWPE in some total hip prostheses and many total knee prostheses, even in the absence of abrasive acrylic debris, and in isolated cases of the latter, fracture; some designs have so exceeded the limits of UHMWPE that the behavior of the prostheses after implantation has been catastrophic. The principal investigators have recently developed new, superior techniques for the molecular weight characterization of UHMWPE and for the measurement of wear under simulated in vivo conditions by debris recovery. These methods have been used to measure the true wear rate and wear mechanisms of UHMWPE, the effects of radiation sterilization and fluid absorption, long-term prognoses for the Charnley hip prosthesis, and to show, in agreement with clinical findings, that relatively severe wear can occur without abrasion by acrylic or other abrasive debris. The occurrence of severe wear is associated with certain features of the structure of UHMWPE, including molecular weight distribution and fusion defects. We propose to develop in our facilities a series of UHMWPE specimens with predetermined microstructural differences, including specimens which (our hypotheses infer) will have superior properties; to make preliminary evaluations of wear resistance in standard geometries and then by total joint simulation, using the methods we have developed and total joint components molded in our facilities; to test for relative fatigue resistance as a function of stress intensity; to fabricate UHMWPE by nonconventional technologies which promise superior microstructure and properties; and to develop nondestructive technologies to monitor the structure of UHMPE in order to assure consistent prosthesis performance.